addSubview SwiftUI View to UIKit UIView in Swift

Question

I have tried to addSubview a SwiftUI View to UIView. self.view.addSubview(contentView)

Error: Cannot convert value of type 'ContentView' to expected argument type 'UIView'

Kindly help me to implement this UI.

import UIKit
import SwiftUI

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        view.backgroundColor = UIColor.lightGray
        
        let contentView = ContentView()
        view.addSubview(contentView) // Error: Cannot convert value of type 'ContentView' to expected argument type 'UIView'
    }


}


struct ContentView: View {
    var body: some  View {
        Text("Hello world")
    }
    
}

Boohoo

View protocol != a UIView – Nest

Watch the very first part of Session 231: Integrating SwiftUI. You need to use UIHostingController. developer.apple.com/videos/play/wwdc2019/231 – Misapprehend

Sorry for the second comment. Since UIHostingController is a UIViewController` and you wish to use addSubview, you'll also need to learn how to use a child view controller (done in UIKit) and part of that involves adding the view as a subview to your parent view. The hosting controllers (one for UIKit, AppKit, and WatchKit) are full controllers, and are easily used for a full screen SwiftUI view. Hope this helps. – Misapprehend

Answer 1

Step 1: Create instances of UIHostingController by using SwiftUI View

struct ContentView : View {
    var body: some View {
        VStack {
            Text("Test")
            Text("Test2")

        }
    }
}

var child = UIHostingController(rootView: ContentView())

Step 2: Add instance of UIHostingController as a child view controller to Any UIKit ViewController

var parent = UIViewController()
child.view.translatesAutoresizingMaskIntoConstraints = false
child.view.frame = parent.view.bounds
// First, add the view of the child to the view of the parent
parent.view.addSubview(child.view)
// Then, add the child to the parent
parent.addChild(child)

You can use the following code to remove a child controller Remove from view Controller

// Then, remove the child from its parent
child.removeFromParent()

// Finally, remove the child’s view from the parent’s
child.view.removeFromSuperview()

Grave

Thanks for your answer, so now I can use SwiftUI in Mac statusbar app. But, you are setting the SwiftUI view's frame by the parent view. I want to do it vice versa, is there a way? And that child's frame will always be zeros unless it has not been set, as far I get. – Scant

This answer is good, thank you. I know Apple is very big on "just rewrite your app from scratch" and "don't connect with any third-party code". But for people on Earth, it would have been nice if Apple just handled all the boilerplate code above invisibly. Then we can gradually switch out UIViews to Views. – Geriatrician

The above doesn't demonstrate what happens when you want to use a SwiftUI View from a UIView directly (i.e. a UIView deep down in the hierarchy wishes to use an existing SwiftUI view, and it doesn't have access to its UIViewController) – Guttle

@Guttle That isn't supported by SwiftUI. You should consider refactoring your code so your view's have access to their controllers. – Photometer

@Grave I am trying to understand why would you need the UIViewController? UIHostingController(rootView: ContentView()).view you can "basically" convert the swiftUI view to UIView, everything seems to work, can you provide reason, why its "not supported"? – Implement